The natural crystalline lens of the eye plays a primary role in focusing light onto the retina for proper vision. However, the natural lens at times is replaced with an artificial lens to make a refractive correction or because of damage or injury to the natural lens. Under these circumstances, the natural lens is surgically removed from the eye.
Surgical procedures which require only a small incision to be made in the eye have been developed for removing the natural lens. In accordance with these procedures, a slender cutting tip of a surgical instrument is inserted through the incision to engage the natural lens. The cutting tip is typically subjected to ultrasonic vibrations to emulsify the lens (e.g., phacoemulsification). The emulsified portions of the lens are then aspirated from the eye through a central bore in the tip. A silicone sleeve surrounds the tip to define an annular conduit for the passage of fluid to cool the tip and irrigate the eye.
During an operation, the surgical instrument is manipulated to remove the entire lens. Because of this movement, the sleeve can at time become pinched between the tip and the tissue of the eye. The frictional contact between the sleeve and the vibrating tip can generate a significant mount of heat in the sleeve. The tissue of the eye is sensitive and can be damaged by the heat in a matter of a few seconds.
Efforts to alleviate the risk of burning the tissue have included such devices as described in U.S. Pat. No. 4,808,154 to Freeman. The Freeman device has longitudinal ribs formed along the interior of the sleeve. The ribs are intended to isolate portions of the wall from the tip to reduce the frictional contact, and provide channels to direct fluid flow about the tip. However, if the conduit becomes partially occluded by material within the eye, the flow of fluid along an entire length of the tip can be lost. Moreover, manipulation of the surgical instrument nay cause the sleeve to twist, which results in the ribs being drawn together thereby closing the channels. Clearly, the partial or complete blocking of the fluid passages will only exacerbate the problems associated with overheating of the surgical site.
U.S. Pat. No. 5,188,589 to Wypych discloses a sleeve wherein the interior surface surrounding the tip is provided with a rough texture of random bangs and pits. The bumps and pits are formed by acid etching or bead or sand blasting of the mold to form a roughened texture having a relieved or sandpaper-like appearance. This construction reduces the frictional contact between the sleeve and the tip, and provides passages (i.e., the pits) through which the fluid can flow about the tip even when compressed. However, the construction of the roughened texture creates blind and constricted passages which increase fluid resistance and hamper proper fluid flow.